It has previously been proposed--see German Pat. No. DE-PS 814 683--to construct piston rings of a sintered powdered light metal which includes additives of heavy metals having high melting temperature. The powdered light metal which is proposed in the aforementioned patent is aluminum powder which has mixed in as a heavy metal, in powder form of fine grain size, magnesium, beryllium, lithium, silicon, copper, nickel, chromium, cobalt, titanium, manganese tungsten, and other heavy metals. The mixture then was sintered at suitable high temperature and under high pressure.
At the time of the aforementioned disclosure, that is, at the time of filing the aforementioned German Pat. No. 814 683, that is, on Oct. 2, 1948, the hot isostatic pressing process was not yet known. Thus, the method used for sintering was the customary hot pressure process in which the powder to be sintered was introduced into a high-pressure, form-stable mold, and compressed by presses operating under high pressure force by plungers to thereby sinter the powder and give it the shape of the mold. This known hot pressing method, by using plungers, can manufacture sintered products of only relatively low density, however. Piston rings which have as a basis aluminum powder with heavy metal fillers therein, and which are made by this well known hot pressure method, then will have a relatively low density, low strength, and, particularly, comparatively low capability of being stretched. Although such piston rings do have good sliding properties, the relatively low expansion or dilation strength, the low ductility and comparatively high brittleness are undesirable, since these piston rings may break already when they are slipped over the the piston to then snap into the piston ring groove in which they are to be seated. There are limits to the thermal loading which piston rings having an aluminum base can tolerate, which thus limits application of the piston rings in internal combustion (IC) engines. In thermally highly loaded IC engines, such piston rings cannot be used without special and additional ways of cooling them. It is also difficult to use such piston rings in IC engines, such as large Diesel engines, which are to be operated with oil having a high sulfur content, such as heavy or residual or heavy fuel oil. Piston rings having an aluminum base are attacked by sulfuric acid which results as a byproduct of combustion within the cylinders of the engine at various locations therein.